Is there a way to tell if MEF created a instace for a Type I exported

My goal is to find any of my viewmodels that are dirty and when they exit the app , I should let them notify.

I can get to an instance based on type by below code but problem is its going to create instances for all view models as I am only interested in the ones which were already created by MEF container
List<Type> viewModelInterfaces = new List<Type>();